The big picture: Plants evolved from green algae
- Cyanobacteria & protist made landfall ~1.2 bya
- plants, fungi and animals ~500 mya
- first forests 385 mya
- Plants evolved from green algae
- Several key ‘derived shared traits’
- Plants support all life on earth
- Oxygen to breath
- food to eat
- new habitats

Green Algae
- Sister group to land plants
- marine and freshwater
- single and multi-cellular
- broad, thick filaments
- some have AoG
- evolved around ~750mya
- Reproductive features:
- Oogonia = egg containing cell
- Antheridium = sperm containing cell


Molecular evidence points at charophytes (freshwater)



Land plants are a monophyletic group

All land plants are embryophytes

- 10 divisions of land plants
- does not include algae
- divisions are species diverse
- Zygote develops into multi-cell embryo
- enclosed in reproductive structure
- algae do not retain embryo
- Land plant & embryophyte terms used interchangeably
Shared traits define land plant evolution


Multi-cellular, Dependent embryos (placental transfer)

Waxy cuticle and stomata


Multi-cellular Gametangia

Photosynthesis with unique pigments (chlorophyll A & B)

Unique cell walls
- Cells walls made of cellulose
- Pectin to fortify cell walls
- Produce cells walls in unique way

Alternation of generations

- Land plants alternate between diplod (2N) and haploid (1N) generations
- diploid = sporophyte
- haploid = gametophyte
- sex cells (1N) make zygote (2N)
- zygote → embryo → sporophyte (all mitosis)
- sporophyte makes spores (1N) by meosis
- spores germinate into gametophyte (1N) by mitosis
- gametophyte makes sex cells (sperm and egg)
- Dominance of different generations key for evolution
First plant group: non-vascular bryophytes (mosses)
- Mosses, hornworts and liverworts
- Fossils of bryophyte spores ~470mya
- Non-vascular; ground hugging carpets
- bodies to thin to support height growth
- Have a rhizoid but not a root
- anchors plant
- does not uptake water
- Need H20 for swimming sperm


Bryophytes have gametophyte dominated life cycle

Vascular plants were the next evolutionary step
- Vascular plants show up ~425mya
- gametophytes become reduced
- Developed a vascular system
- grow taller = get light
- xylem and phlome conduct
- Developed leaves & roots
- better access to resources
- First vascular plants lacked seeds
- sperm still needed to swim
- ferns and lycophytes

Lycophytes: First vascular plants

- Independent, branched sporophyte
- Lignified vascular tissue
- Leaves are microphylls
- one vein per leaf (unique trait)
- Lycophyte forests (30m) once existed
Ferns
- Whisk Ferns, Equisetum & Ferns
- New Gaga genus with 19 species
- “We wanted to name this genus for Lady Gaga because of her fervent defense of equality and individual expression” Pryer @ Duke University


Seedless vascular plants have free-living separate generations
- Sporophyte: The fern you see in the woods
- Gametophye: independent haploid generation
- start out female or bisexual
- Derived Trait - remember how a moss looks!
- What does natural selection favor diploid dominant life cycles?

Seed plants were the next evolutionary step
- Seeds changed the course of plant evolution
- Seed plants show up ~360 mya
- climate became drier
- Seeds consists of embryo & nutrients
- surrounded by protective coat
- seeds can be dispersed long distances
- less dependence on water
- 2 living seed lineages
- gymnosperms (naked seed)
- angiosperms (covered seed = fruits)

Why seeds matter so much…
- Before seeds, spore was only protective structure
- super small so spread all over Earth
- Seeds can remain dormant for a long time
- Gymnosperms: seeds exposed on sporophylls, form cones
- Angiosperms: seeds enclosed inside fruits

4 living lineages of gymnosperms
- Cycads: 300 living species
- earliest evidence of insect pollination
- Cycads and dinosaurs lived together
- Gnteophytes: small and super weird group
- Ginkos: Ginkgo biloba is only species left!
- Conifers: ~600 species (cones)
- evergreen and deciduous
- leaves are needles or scales

Flowering plant diversity
- Most diverse living group of plants
- 14,000 genera, 250,000 species
- 2 classes: Moncots and Dicots
- monocots = one seed leaf in embryo
- dicots = two seed leaf in embryo

Angiosperm evolution: Bugs and animals

